1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor substrate including a single crystal semiconductor layer. The present invention also relates to a method for manufacturing a semiconductor device using a semiconductor substrate including a single crystal semiconductor layer.
2. Description of the Related Art
In recent years, integrated circuits using a silicon-on-insulator (SOI) substrate instead of a bulk silicon wafer have been developed. A feature of a thin single crystal silicon layer formed over an insulating layer can be taken advantage of to form a completely electrically isolated semiconductor layer of a transistor in an integrated circuit and to form a completely depleted transistor. Accordingly, a semiconductor integrated circuit having high added values such as high integration, high-speed operation, and low power consumption can be realized.
A separation-by-implanted-oxygen (SIMOX) technique and a bonding technique are well known as techniques for manufacturing SOI substrates. A SIMOX technique refers to a technique in which oxygen ions are implanted at high concentration to a predetermined depth in a single crystal silicon wafer and heat treatment is performed at 1300° C. or higher, thereby forming a buried oxide layer (hereinafter referred to as a “BOX layer”) of silicon oxide. In this technique, a single crystal silicon layer is formed by formation of a BOX layer in a bulk single crystal silicon wafer. Due to implantation of oxygen ions, the technique has a disadvantage in that the crystal structure of the single crystal silicon layer is greatly damaged.
A bonding technique refers to a technique in which two single crystal silicon wafers are bonded to each other with an insulating film interposed therebetween and one of the single crystal silicon substrates is divided, thereby forming a thin single crystal silicon layer over the other single crystal silicon wafer with the insulating film interposed therebetween (for example, see Reference 1: Japanese Published Patent Application No. H5-211128).
In Reference 1, first, H+ ions (protons) are implanted into a single crystal silicon wafer to form a microbubble layer therein in order to cleave the single crystal silicon wafer. Next, a silicon wafer which is covered with an oxide and the single crystal silicon wafer in which the microbubble layer is formed are disposed in contact with each other and subjected to heat treatment or electrostatic treatment, thereby bonding the two single crystal silicon wafers to each other. Then, heat treatment is performed to cleave the single crystal silicon wafer along the microbubble layer, thereby forming a thin single crystal silicon layer. A technique of forming a microbubble layer where ions such as hydrogen ions are implanted at high concentration in a semiconductor substrate and dividing the substrate along this layer is referred to as a Smart Cut (registered trademark) method, a hydrogen ion implantation method, or the like.
There are known methods for manufacturing a semiconductor substrate having an SOI structure by forming a single crystal silicon layer over a substrate of a different kind of material such as a glass substrate with the use of such a hydrogen ion implantation method as described above (see References 2 to 5). Reference 2 discloses a method for manufacturing a semiconductor device using a single crystal silicon layer which is formed over a light-transmitting substrate by being separated from a single crystal silicon wafer with the use of a hydrogen ion implantation method (Reference 2: Japanese Published Patent Application No. 2000-150905).
Reference 3 discloses a method for manufacturing an SOI substrate which does not require any heat treatment at a high temperature exceeding 800° C. (Reference 3: Japanese Published Patent Application No. 2005-252244). After a semiconductor wafer is bonded to a glass substrate, heat treat is performed at a temperature not exceeding 600° C. Accordingly, the semiconductor wafer is cleaved along a microbubble layer to separate a semiconductor thin film from the semiconductor wafer, thereby forming a semiconductor thin film layer over the glass substrate. After this separation step, laser light irradiation is performed to improve crystal quality of the semiconductor thin film layer and to strongly bond the semiconductor thin film layer and the glass substrate.
Reference 4 discloses the following: bonding a silicon wafer and a glass substrate; dividing the silicon wafer where ions are implanted, by microwave irradiation; and cooling two substrates to 400° C. or lower in microwave irradiation, when a silicon wafer is bonded to a substrate of a different kind of material, in order to prevent a bonding structure between the two substrates from being destroyed with a temperature increase in dividing the silicon wafer, due to a difference in coefficient of thermal expansion between the silicon wafer and the substrate (Reference 4: Japanese Published Patent Application No. 2001-244444).
Reference 5 discloses that a plurality of single crystal silicon layers is bonded to one glass substrate in a tiled manner (Reference 5: Japanese Translation of PCT International Application No. 2005-539259). In Reference 5, a semiconductor substrate (donor substrate) is divided not by heat treatment but by separation through destruction with a mechanical means such as a nitrogen gas flow (see page 12, lines 40 to 44).